There is now strong evidence that endemic HTLV-II infection is present in American Indians of New Mexico. Data from blood donors would suggest that 1-2% of indians with no previously-known risk factors for HTLV infection has been exposed to HTLV-II; firthermore, distant indian ancestry or indian sexual partners are now emerging as independent risk factors for HTLV-II infection in non-indians in our region. Despite this HTLA-II endemia, no evidence for increased rates of hairy cell leukemia, mycosis fungoides or chronic lymphocytic leukemia have emerged by study of patients from the New Mexico Tumor Registry. Limited and directed probing of the NMTR for indian patients with common lymphoid neoplasms has revealed preliminary evidence that HTLV-II provirus is present in the lymphoma cells of a patient with non-Hodgkins lymphoma. This patient has two HTLV-seropositive children. A study is proposed to answer the following questions. (1) What is the actual prevalence of HTLV-II infection in indians in our region? (2) Are indian patients with lymphoid leukemia or non-Hodginkins lymphoma at increased risk for HTLV-II infection? (3) How many HTLV-II-infected indian leukemia and lymphoma patients have HTLV-II provirus in "single- copy" abundance in their tumors? We propose the following methods to address these questions. (1) Perform blinded seroprevalence studies on (A) 200-300 unselected outpatients and (B) 200-300 obstetric patients presenting to the Albuquerque IHS hospital, using reagents capable of distinguishing the two viruses. (2) Trace all (A) living indians with leukemia and lymphoma in New Mexico through the NMTR and offer them serologic testing for HTLV-I and II, and (B) trace all available pathologic specimens on all deceased indians with leukemia or lymphoma and perform PCR on the archived tumors. The goal of this study is to define any potential of HTLV-II to induce lymphoid neoplasms in the HTLV-II-endemic populations.